Daily Olympiad: Biology - Ecology Environment [20260511]

Solution

Correct: C

The pyramid of energy follows the 10% rule (Lindeman's ten percent law). Energy at the producer level is 10,000 kcal/m²/year. Primary consumers receive about 10% of that, i.e., 1,000 kcal/m²/year. Secondary consumers receive 10% of primary consumers, i.e., 100 kcal/m²/year. Tertiary consumers receive 10% of secondary consumers, i.e., 10 kcal/m²/year. Therefore, the energy available to tertiary consumers is approximately 10 kcal/m²/year.

Solution

Correct: D

The species-area relationship is a power function: S = cA^z, where S is species richness, A is area, and z is the slope. When plotted on a log-log scale, the relationship becomes linear. However, the z-value varies depending on habitat type and isolation; it is not always 0.5. The species-island relationship states that larger and less isolated islands have higher species richness (Island Biogeography Theory by MacArthur and Wilson), so distant islands generally have lower species richness than closer ones. The relationship does hold for large areas and is used to predict species loss due to habitat fragmentation.

Solution

Correct: B

Pioneer species are the first organisms to colonize barren or disturbed habitats. On bare rock surfaces, lichens and mosses are the typical pioneer species because they can withstand extreme conditions, can fix nitrogen (lichens), and can break down rock to begin soil formation through weathering. Over time, they create a thin layer of soil that allows mosses and later herbaceous plants to establish. Oak trees and deciduous shrubs are part of later successional stages or climax communities, not pioneer stages.

Solution

Correct: A

The edge effect refers to the changes in population or community structures that occur at the boundary of two or more different habitats. It is characterized by an increased biodiversity at habitat edges because species from both adjacent habitats, as well as species specifically adapted to edge conditions, can coexist. This is a well-documented phenomenon in landscape ecology and is relevant in conservation biology for designing nature reserves and wildlife corridors.

Solution

Correct: C

The Intermediate Disturbance Hypothesis, proposed by Connell (1978), states that species diversity is maximized at intermediate levels of disturbance. At low disturbance, competitive exclusion by dominant species reduces diversity. At very high disturbance, only r-selected species survive, and diversity decreases. An intermediate disturbance prevents any single species from dominating while allowing both r-selected and K-selected species to persist, thereby maximizing diversity.

Solution

Correct: C

While N₂ and O₂ are the most abundant gases in the atmosphere, they are largely transparent to infrared radiation and do not significantly contribute to the greenhouse effect. CO₂, though present in much smaller concentrations (~0.04%), is a major greenhouse gas because it absorbs and re-emits infrared radiation, trapping heat in the atmosphere. Other greenhouse gases include methane (CH₄), water vapor, and nitrous oxide (N₂O), but CO₂ is the most significant anthropogenic greenhouse gas driving global warming.

Solution

Correct: B

Ecological efficiency is calculated as the ratio of energy or biomass at one trophic level to the energy or biomass at the previous (lower) trophic level, expressed as a percentage. Here, energy transfer efficiency from producers to primary consumers = (Biomass of primary consumers / Biomass of producers) × 100 = (1000 / 10000) × 100 = 10%. This aligns with Lindeman's ten percent law, which states that only about 10% of energy is transferred from one trophic level to the next.

Solution

Correct: C

r-selected species (opportunistic species) are characterized by high reproductive rates, small body size, short generation time, high dispersal ability, and rapid colonization of disturbed or new habitats. They invest minimal parental care and produce many offspring. Long generation time is a characteristic of K-selected species, not r-selected species. K-selected species have slow reproduction, larger body size, longer generation time, and invest heavily in a few offspring.

Solution

Correct: B

BOD is defined as the amount of dissolved oxygen required by aerobic biological organisms to break down organic material present in a given water sample at a certain temperature over a specific time period (usually 5 days at 20°C). A high BOD indicates that a large amount of organic matter is present in the water, which is decomposed by aerobic bacteria that consume dissolved oxygen, leading to oxygen depletion and potentially causing fish kills. BOD is a key parameter in assessing water pollution and eutrophication.

Solution

Correct: C

According to the competitive exclusion principle (Gause's Law), two species competing for exactly the same resources cannot stably coexist in the same habitat—one will eventually outcompete and eliminate the other. Therefore, for stable coexistence, species must exhibit niche differentiation or niche partitioning, meaning their niches differ in at least one dimension such as food source, time of activity, spatial habitat use, or foraging behavior. This reduces direct competition and allows both species to persist.

Solution

Correct: C

The pyramid of energy is always upright because energy is lost at each successive trophic level through metabolic processes and heat loss, following the first law of thermodynamics. Unlike pyramids of numbers or biomass, which can be inverted or spindle-shaped depending on the ecosystem (e.g., a single large tree supporting many insects gives an inverted pyramid of numbers; a forest ecosystem can show an inverted pyramid of biomass), the pyramid of energy always decreases from producers to top consumers.

Solution

Correct: B

Eutrophication is the process by which a body of water becomes enriched with excessive nutrients, particularly nitrogen and phosphorus, often from agricultural runoff, sewage discharge, or fertilizer leaching. These nutrients stimulate excessive growth of algae and aquatic plants (algal blooms). When these organisms die, their decomposition by aerobic bacteria consumes dissolved oxygen, leading to hypoxic or anoxic conditions that kill fish and other aquatic organisms. This process is called cultural or anthropogenic eutrophication.

Solution

Correct: B

The classical model of primary succession on bare rock (e.g., after glacial retreat or volcanic eruption) begins with pioneer species such as lichens and mosses that can colonize bare rock. These organisms help break down rock and accumulate organic matter, forming a thin soil layer. This allows herbaceous plants (ferns, grasses) to establish, followed by shrubs, and eventually trees. The final stage is the climax community, which in temperate regions is typically a deciduous or mixed forest. Lichens are typically the first pioneers, not mosses alone.

Solution

Correct: B

An inverted pyramid of biomass occurs in certain aquatic ecosystems, particularly open ocean or deep water ecosystems, where the biomass of producers (phytoplankton) is very low compared to the biomass of consumers (zooplankton, small fish, and large predators). This is because phytoplankton have a very rapid turnover rate—though their total biomass is small, their productivity (rate of biomass production) is high. The pyramid of numbers is also inverted in such ecosystems, but the pyramid of energy remains upright.

Solution

Correct: A

The rivet-popper hypothesis, proposed by Paul Ehrlich, compares biodiversity loss to the removal of rivets from an airplane. Just as an airplane can lose a few rivets without failing but will eventually crash if too many are removed, an ecosystem can tolerate some species loss but will eventually collapse when the loss exceeds a critical threshold. This metaphor emphasizes that species are not redundant and that each species plays a role in maintaining ecosystem integrity, function, and resilience. It underscores the importance of conserving biodiversity to prevent ecosystem collapse.